U.S. Pat. No. 5,086,764 discloses various forms of wound dressings in which an absorbent fabric 12 is located either in a wound cavity beneath a base sheet 14 or directly above an aperture 18 in that base sheet. In either case, the absorbent fabric 12 is removable or separable from the base sheet 14 so that it may be easily changed without disturbing that sheet when the fabric becomes saturated. In some versions, a back sheet 38 extends over the absorbent fabric and is secured thereto by a pressure-sensitive coating 40.
Soft, compressible, highly absorbent and hydrophilic foams are also known for medical and dental use as disclosed, for example, in U.S. Pat. No. 3,903,232. While such foams may be of different polymeric compositions, the polyurethane foams disclosed in the aforementioned patent are exceptionally soft and hydrophilic, expanding quickly as they absorb aqueous fluids.
Other U.S. patents illustrating the state of the art are U.S. Pat. Nos. 5,146,362, 5,603,946, 5,244,457, 4,907,570, and 5,056,510.
A main aspect of the present invention lies in providing an improved wound dressing for preventing pooling of liquid in a draining or exuding wound while at the same time protecting the wound against contamination and maintaining the surrounding skin surfaces in a relatively dry state. The dressing utilizes a soft, hydrophilic polymeric foam layer that readily expands into a wound cavity as it absorbs wound exudate.
In the dressing of this invention, the absorbent foam layer is permanently secured to the backside of an elastomeric base film. The base film is vapor-permeable but liquid impermeable except for one or more generally central openings through which a portion of the underside of the foam layer is exposed. A pressure-sensitive adhesive coats the underside or bodyside surface of the film for securing the dressing to body surfaces at a wound site. The adhesive coating (or each such coating) of the base film is discontinuous or micro-porous so that it does not block the transmission of moisture vapor through the film.
An elastomeric backing layer extends over the back surface of the foam layer but ideally is not directly attached or adhered to the foam layer. The lack of adherence or attachment is important because it enhances conformability of the dressing to anatomical contours, and to changes in such contours as a patient moves about, and allows limited displacement of the foam layer away from the backing layer and expansion into a wound cavity when the dressing is in use. If desired, the outermost surface of the elastomeric backing layer may be covered by a soft foraminous foam layer having a multiplicity of wide openings, preferably taking the form of a stretchable foam grid, to assist in the handling, delivery, and application of the dressing at a wound site.
Other features, advantages and objects of the invention will become apparent from the specification and drawings.